error[E0277]: the trait bound `Test: GraphQLObject<__S>` is not satisfied
  --> fail/union/struct_non_object_variant.rs:10:14
   |
10 | #[graphql(on Test = Character::a)]
   |              ^^^^ the trait `GraphQLObject<__S>` is not implemented for `Test`
   |
   = help: the following other types implement trait `GraphQLObject<S>`:
             <&T as GraphQLObject<S>>
             <Arc<T> as GraphQLObject<S>>
             <Argument<'a, S> as GraphQLObject<S>>
             <Box<T> as GraphQLObject<S>>
             <EnumValue as GraphQLObject<__S>>
             <SchemaType<'a, S> as GraphQLObject<S>>
             <juniper::meta::Field<'a, S> as GraphQLObject<S>>
             <juniper::schema::model::DirectiveType<'a, S> as GraphQLObject<S>>
             <juniper::schema::model::TypeType<'a, S> as GraphQLObject<S>>